Reproductive Cycle of the Gila Monster, Heloderma suspectum, in Southern Arizona

Abstract

The family Helodermatidae contains two species, the Gila monster, Heloderma suspectum and the Mexican beaded lizard, Heloderma horridum, which are the only venomous lizards known (Stebbins, 1985). The range of the Gila monster extends from southwestern Utah to northern Sinaloa and southwestern New Mexico to the Colorado River from sea level to around 1520 m (Stebbins, 1985). Aspects of its biology have been studied (Bogert and Martin Del Campo, 1956; Lowe et al., 1986). However, to our knowledge, there are only anecdotal accounts of its reproductive biology. The purpose of this report is to provide information on the reproductive cycle of H. suspectum in southern Arizona. This study was based on examination of the reproductive organs of 112 H. suspectum, 100 of which were from the vicinity of Tucson, Pima County, Arizona (32?9'N, 110?59'W, ca. 743 m elevation). Two of these were from Cochise County and Pinal County. These 102 specimens were collected during 1964-1967 and 1985 and were deposited in the herpetology collection of the Natural History Museum of Los Angeles County (LACM) 142910-142964, 142966142967, 142969-142972, 142976-143016). Lizards were sacrificed with an intraperitoneal injection of sodium pentobarbital (Nembutal? Sodium, Abbott Laboratories, North Chicago, Illinois U.S.A.) and were preserved in Bouin's fixative (Humason, 1979). They were later transferred to 70% ethanol for storage. A sample of 10 H. suspectum (formalin fixed and stored in ethanol) from the University of Arizona herpetology collection (UAZ) 7196, 7207, 10110, 25635, 31173, 3506935070, 42715-42716, 44318 were examined. All were from the Tucson area except for UAZ 42716 which was from Sonora, Mexico. Right testis width was measured (in situ) and a ratio of right testis width/snout-vent length (SVL) was calculated. The condition of the ovary was noted. All enlarged oocytes and oviductal eggs were counted. Pieces of testes, epididymides, vasa deferentia, and selected ovaries were removed for histological examination. Sections were cut at 6 p.m with a rotary microtome and stained with hematoxylin and eosin.